Fuel cells are used as an electrical power source in many applications. In particular, fuel cells are proposed for use in automobiles to replace internal combustion engines. A commonly used fuel cell design uses a solid polymer electrolyte (“SPE”) membrane or proton exchange membrane (“PEM”) to provide ion transport between the anode and cathode.
In proton exchange membrane type fuel cells, hydrogen is supplied to the anode as fuel and oxygen is supplied to the cathode as the oxidant. The oxygen can either be in pure form (O2) or air (a mixture of O2 and N2). PEM fuel cells typically have a membrane electrode assembly (“MEA”) in which a solid polymer membrane has an anode catalyst on one face, and a cathode catalyst on the opposite face. The anode and cathode catalyst layers of a typical PEM fuel cell are typically thin films formed by dried inks. Each electrode has finely divided catalyst particles (for example, platinum particles) supported on carbon particles to promote oxidation of hydrogen at the anode and reduction of oxygen at the cathode. Protons flow from the anode through the ionically conductive polymer membrane to the cathode where they combine with oxygen to form water which is discharged from the cell. The MEA is sandwiched between a pair of electrically conductive porous gas diffusion layers (“GDL”) which, in turn, are sandwiched between a pair of non-porous, electrically conductive elements or plates. The plates function as current collectors for the anode and the cathode, and contain appropriate channels and openings formed therein for distributing the fuel cell's gaseous reactants over the surface of respective anode and cathode catalysts. In order to produce electricity efficiently, the polymer electrolyte membrane of a PEM fuel cell must be thin, chemically stable, proton transmissive, non-electrically conductive and gas impermeable. In typical applications, fuel cells are provided in arrays of many individual fuel cells arranged in stacks in order to provide high levels of electrical power. Although the catalyst layers used in fuel cells work reasonably well, such layers tend to be expensive.
To reduce the cost of fuel cells, it is desired to reduce the number of parts and manufacturing processes. Each cell requires a seal for each reactant and coolant as well as tunnels (openings past the seal) to allow reactants and coolant to pass to and from their respective headers. The sealing is typically accomplished with a molded elastomeric seal for the reactants and welding of stamped metal plates to seal coolant. The tunnel features are typically part of the plate, but with stamped plates, this also puts these features on the other side of the plate which is not always desirable. One issue with molded seals is the cost of mold cavities and long cure times which lead to an expensive part. Cure-in-place seal materials can be dispensed onto the plate or sub-gasket, but this process is slow. The dispensed seal also presents challenges at knit lines and intersections to maintain a consistent seal thickness especially for the small repeat distances desired for automotive fuel cells. The plate welding process, including fixturing the two plate halves together, can be slow and costly. The need to weld plate halves together can also limit plate metal and coating choices.
Accordingly, there is a need for improved methods for forming seals that are applicable to fuel cells and fuel cell stacks.